Various methods, and filtration installations that operate according to those methods, are known for filtering liquid products, such as drinks, including beer.
A known way to filter drinks is the conventional precoat filtration method. In this method, the unfiltrate comprises the product to be filtered and a filtration aid. The filter structure consists essentially of a filter sheet formed by the filtration aid or of a filter cake.
Another known method involves filtering with a membrane filter structure. This method requires no filtration aid. Such membrane filtration systems or filtration installations offer fundamental advantages including ease of automation, as a result of its underlying simplicity, low operation costs, provided the product or filtration material is easily filterable, the ability to filter in continuous mode, powder-free and dust-free operation, arising from avoidance of filtration aids such as kieselguhr, polymer filtration aids, etc., and avoiding the need for filter sludge disposal.
Membrane filtration systems/installations also have disadvantages, including high investment costs, lengthy regeneration times for the filtration installation concerned, inability to adapt to fluctuating unfiltrate qualities, because there is no filtration aid to proportion, relatively high operating costs if the product has poor filterability, and poor plant availability if frequent regeneration of the filter structure or filter elements and their membranes is necessary.
It is also often the case that filtration using membrane filter structures or membrane filters is not economical if, because of the unfiltrate quality, the permeability of the filter structure rapidly decreases as the membranes become clogged with unfiltrate residues or with lees. In these cases, at least backwashing with product, filtrate, or water will be necessary. This entails a loss of time and product. It is also frequently unsuccessful. As a result, the entire filtration installation must be shut down and regenerated with a cleaning or flushing agent.
A further disadvantage is that the physical and chemical strain on the filter elements and/or on their membranes during the regeneration process is many times greater than it is during the filtration process. During actual filtration, the filter elements and their membranes are exposed only to minimal strain. This is because the filtration material flows slowly. The opposite is true during regeneration. Consequently the service life of the filter elements is determined not by the number of production hours but primarily by the number of regeneration cycles.